In a message dated 08/07/02 05:00:59 GMT Daylight Time, Peter Borst writes:

<< The proportion of workers with fully activated ovaries in normal
 queenright colonies is extremely low, approximately 0.01%.
  >>

So in a typical queenright colony at this time of year there may be as many
as half a dozen laying workers.  I think it was Aebi who wrote (although I
don't know his source) that maybe 1% of laying workers can lay female eggs.
So maybe something in the region of one colony in 20 will have a laying
worker producing female eggs.

That is one of several (more likely) explanations for something I found this
year: a sealed queen cell several inches above a good queen excluder with no
other brood above the QE.  The queen was in full lay below the QE.

Chris